Telephone companies own the telephone network wires outside of privately owned buildings, while the owners of the buildings own the telephone wiring inside the buildings. An interface, known as a customer bridge, is provided at the entrance to the building, where the telephone company wires meet the building wires. The customer bridge has a customer connector assembly to which the customer's telephone lines are all electrically coupled. The connector assembly may include any of a variety of known terminals or connectors for attaching customer lead wires.
The customer bridge also includes a network interface device (NID). The NID typically includes a jack (which may be a standard RJ11 jack) which is coupled to the external telephone network. The customer wires typically terminate in a mating RJ11 plug, which is normally inserted in the RJ11 jack of the NID.
Nominally, the telephone lines operate at low voltage conditions, but a high voltage condition may occur, for example, due to lightning. To protect a user who may be connecting or disconnecting telephone lead wires to/from the customer interface connectors, Underwriters Laboratories (UL) requires that the customer interface be disconnected from the external network by unplugging the RJ11 plug from the RJ11 jack at the entrance to the property, before performing work on the internal building wires. This requirement is enforced by way of warning labels and instructions. Thus, it is up to the individual who is handling the wires to read the warning/instructions and execute this safety procedure.